Vacuum tube oscillator



Feb. 6, 1940. v D 'PA$MA 2,189,402

VACUUM TUBE OSCILLATOR Filed June 5, 1938 INV EN TOR. DOUWEPASMA ATTORNEY.

PatentedFeb. c, 1940 "UNITED STATES VACUUM TUBE OSCILLATOR Douwe Pasma, Eindhoven, Netherlands, assignor, by mesne assignments, to Radio Corporation of America, New. York, Delaware N. Y., a corporation of Application June 3, 1938, Serial No. 211,495- In the Netherlands August 21, 1937 4 Claims.

relatively to the cathode of the generator valve so that the filament-cathode capacity, which is connected in parallel with part of the frequencydetermining circuit of the generator, varies. In order to obviate the harmful effects of this variation in capacity it has previously been proposed to supply the filament via two choke coils so that the filament-cathode capacity is connected in series with a high impedance parallel to part of the oscillatory circuit. It has, however, been found in practice that this precaution does not suflice to completely neutralise the disadvantage indicated before.

According to the invention, it is therefore proposed that in the circuit arrangement in which the cathode is supplied via two choke coils the cathode should be connected to the filament through a condenser whose capacity is high as compared with the internal capacity between the cathode and the filament. Preferably, use is made of a condenser having a capacity of 5000,11. F. i

In order that the invention may be clearly understood and readily carried into efiec-t one embodiment thereof will now be described more fully with reference to the accompanying drawing.

a point of the inductance coil 5. The tuning circult is earthed on one side.

The filament supply voltage is supplied by a source of voltage I the voltage of which is supplied to the filament via two bifilar wound conductors 8. The positive terminal of the source of anode voltage (not shown) is connected to the anode via a choke coil 9, the series combination of the choke coil 9 and the source of anode voltage being bridged by a condenser In which constitutes a short-circuit for the oscillations to be generated.

The circuit described so far has the disadvantage that when used as a local generator in a superheterodyne receiver the phenomenon described above occurs. This phenomenon is due to the fact that the series combination of the cathode-filament capacity with the coils constituted by the bifilar wound conductors 8 is connected in parallel with part of the oscillatory circuit. Any variation of the said capacity will consequently affect the frequency of the oscillations generated and since the filament is set into vibration relatively to the cathode under the influence of the sound oscillations reproduced in the loudspeaker, a periodical variation in the value of the filament-cathode capacity will occur. By arranging between the cathode and the filament a condenser ll whose capacity is high as compared with the cathode-filament capacity, the influence of these variations on the frequency of the oscillations generated is practically neutralised completely, since the cathode-filament capacity is negligible with respect to the capacity of the condenser.

What I claim is:

1. An oscillation generator comprising an electron discharge tube provided with a grid, an anode, an indirectly heated cathode and a heatable filament for said cathode, a frequency determining circuit connected between the anode and the control grid, a connection from the cathode to an intermediate point of said circuit, means for maintaining the heatable filament at a radio frequency potential and above ground, and a condenser connected between the cathode and fila ment, the capacity of said condenser being high as compared with the internal capacity between cathode and filament.

2. An oscillation generator comprising an electron discharge tube provided with a grid, an anode, an indirectly heated cathode and a heatable filament for said cathode, a frequency detel-mining circuit connected between the anode and the control grid, a connection from the cathode to an intermediate point of said circuit, means connected to the filament for maintaining the same above zero radio frequency potential, said means comprising a pair of bifilar windings through which the heating current is fed, and a denser connected between the cathode and filament for maintaining the cathode above zero radio frequency potential, the capacity of said condenser being high as compared with the internal capacity between cathode and filament.

3. An oscillation generator comprising an electron discharge tube provided with a grid, an anode, an indirectly heated cathode and a heatable filament for said cathode, a frequency determining circuit connected between the anode and the control grid, a connection from the oathode to an intermediate point of said circuit, means connected to the filament for maintaining the same above zero radio frequency potential, said means comprising a pair of bifilar windings through which the heating current is fed, and a condenser having a capacity of at least 5000 F. connected between the cathode and filament for maintaining the cathode above zero radio frequency potential, said capacity being high as compared with the internal capacity between cathode and filament.

4. An oscillation generator comprising an electron discharge tube provided with a grid, an anode, an indirectly heated cathode and a heatable filament for said cathode, a frequency determining circuit connected between the anode and the control grid, 2. connection from the cathode to an intermediate point of said circuit, means connected to the filament for maintaining the same above zero radio frequency potential, and means connected between filament and cathode for maintaining the cathode above zero radio frequency potential.

DOUWE PASMA. 

